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Featured researches published by Joachim Dierker.
Archive | 2004
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
Radiation exposure and image quality in X-ray diagnostic radiology , Radiation exposure and image quality in X-ray diagnostic radiology , کتابخانه دیجیتالی دانشگاه علوم پزشکی و خدمات درمانی شهید بهشتی
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
The radiological image is composed of the spatial variations of a physical quantity, e.g. the X-ray fluence at the input of the imaging chain (radiation image). When using a film-screen system then this spatial variation is represented by the resulting distribution of the optical density on the film (radiograph), when using a digital imaging system it is – after corrections of the raw data with reference to IEC 62494 (see IEC 62494, 2008) and postprocessing – shown by the resulting grey-scale values e.g. on the monitor of the viewing station (X-ray image). The radiological image represents the projection of the spatial distribution of the patient tissue components within the field of view. Visualisation of important details requires separation of the ‘structures of interest’ against the ‘background’ (e.g. in mammography, micro-calcifications in the breast glandular tissue). Loosely speaking, the difference between structures of interest and background is referred to as the signal.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
Dose output Y100 of X-ray tube assemblies with W/Re-anode at a target angle of 10° and various additional filtration; focus distance of 100 cm (the figure is equivalent to Fig. 10.3)
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
X-rays are produced when a beam of fast electrons strikes a target. The electrons lose, on this occasion, most of their energy in collisions with atomic electrons in the target, causing ionisation and excitation of atoms. In addition they can be sharply deflected by the electric field of the atomic nuclei, thereby losing energy by emitting X-ray photons.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
Typical geometrical and physical characteristics of anti-scatter grid Pb 12/40 Typical geometrical and physical characteristics of anti-scatter grid Pb 13/75 Typical geometrical and physical characteristics of anti-scatter grid Pb 15/80
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
The physical characteristics of the radiation source and the exposure parameters, which together determine the radiation quality, are the anode material of the X-ray tube and the filtration of the primary radiation beam, the X-ray peak tube voltage selected, its temporal course (e.g. especially at short exposure times or, in pulsed exposure techniques, its rise and drop) and the inherent waveform of the tube voltage (2-, 6-, 12-, multi-pulse or DC). The radiation quality (i.e. the photon energy spectrum) influences both patient dose and image quality. An increase in the X-ray tube voltage for a certain anode-filter combination at a definite image receptor dose (see Sect. 5.2) will result in an increased penetration of the X-ray beam and consequently in a reduction of the absorbed dose and the contrast observed in the image.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
The knowledge of the relationship that links image quality and radiation dose is a prerequisite to any optimisation of medical diagnostic radiology, because — according to the ALARA concept — the dose received by the patient during a radiological examination should be kept “as low as reasonably achievable” (see preface). The image quality and dose required for a successful and reliable diagnosis depends on physical parameters such as contrast, resolution and noise, the constitution of the patient, the viewing conditions (Brandt et al. 1983) and also on the characteristics of the observer that assesses the image. In Chap. II.7 (see Fig. II.7.2) the importance of the coordination of these influencing quantities has been pointed out. Furthermore, one should take into consideration that reducing the system noise by increasing the dose will not always improve task performance. This observation indicates that the imaging process might be optimised by accepting a higher system noise (e.g. in paediatrics). The following shows how exposure parameters can be adapted to the medical indication.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
The attenuation properties of the various kinds of tissue in the patient’s body with respect to X-ray photons in the energy range of about 10 keV to 150 keV is determined principally by the photoelectric effect and Compton scattering (see Chap. II.2). Therefore, in X-ray imaging, photons emitted from the focal spot of the X-ray tube enter the patient, where they may be absorbed, transmitted without interaction (primary photons) or scattered (secondary photons). The radiation image is formed from the emergent primary photons while impaired by the secondary photons (see Chaps. II.5 and III.2). By the interaction of all these photons with a suitable image receptor, the radiographic image is built up. So the X-ray image consists of a two-dimensional projection of the attenuating properties of the tissues in the three-dimensional volume of the patient’s body along the path of the X-ray photons superimposed by scattered radiation.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
In X-ray diagnostic radiology there are essentially two reasons for determining radiation doses to patients. Firstly, knowledge of the absorbed doses to tissues and organs in the patient is needed to estimate the associated radiation risk. Secondly, this knowledge plays a significant role in the optimisation of image quality versus radiation exposure and therefore in the process of setting and checking standards of good practice.
Archive | 2012
Horst Aichinger; Joachim Dierker; Sigrid Joite-Barfuß; Manfred Säbel
Diagnostic X-ray spectrum generated by a W/Re anode Target angle: 10° Total filtration: 2.5 mm Al Reference focal distance: 100 cm X-ray tube voltage: 40 kV